Package com.github.basking2.sdsai.itrex.iterators

Class ParallelIteratorIterator<T>

java.lang.Object

com.github.basking2.sdsai.itrex.iterators.ParallelIteratorIterator<T>

All Implemented Interfaces:

Iterator<T>

Direct Known Subclasses:

PrefetchingIterator

public class ParallelIteratorIterator<T>
extends Object
implements Iterator<T>

Fetch from a set of iterators concurrently and return the first ready element. Similar to IteratorIterator, this aggregates a set of iterators.

Constructor Summary

Constructors

Constructor	Description
ParallelIteratorIterator(Executor executor, int queueSize, List<Iterator<T>> inputs)
ParallelIteratorIterator(Executor executor, int queueSize, List<Iterator<T>> inputs, Consumer<Throwable> reportError)	Constructor.

Method Summary

Modifier and Type	Method	Description
boolean	hasNext()	Check if a new result should be expected and fetch with a call to next().
T	next()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface java.util.Iterator

forEachRemaining, remove

Constructor Details

ParallelIteratorIterator

public ParallelIteratorIterator(Executor executor,
 int queueSize,
 List<Iterator<T>> inputs)

ParallelIteratorIterator

public ParallelIteratorIterator(Executor executor,
 int queueSize,
 List<Iterator<T>> inputs,
 Consumer<Throwable> reportError)

Constructor.

Parameters:

executor - The executor that provide the parallelism.

queueSize - The depth of the queue to use for iterated results. For performance reasons the actual depth of cached results is the length of the inputs + queueSize. The reason for this is that in some very contrived timing situations all iterators can begin producing values and exhaust the last queue space. Typically only 1 producing iterator will do this.

inputs - The list of input iterators. Each iterator may be accessed in parallel with another. If iterators share resources, this behavior must be accounted for.

reportError - A way to communicate errors.

Method Details

hasNext

public boolean hasNext()

Check if a new result should be expected and fetch with a call to next(). This first checks if the internal queue has a cached result, and returns true if it does. Otherwise, each actor is checked if it still has results to fetch. If any returns true, this returns true. Finally, the results queue is re-checked in case an actor published a result between the time we first checked the results queue and then checked each actor individually.

Specified by:

hasNext in interface Iterator<T>

Returns:

True if there are more elements to fetch or retrieve out of the cache queue. False otherwise.

next

public T next()

Specified by:

next in interface Iterator<T>